Microbial Metabolism Questions and Answers

Answer: A

Correct answer: all of these

Passive and facilitated diffusion both move solute down its electrochemical gradient, so they need none of the three: no metabolic energy, and no ability to concentrate or accumulate solute against a gradient. Facilitated diffusion differs from simple diffusion only in using a carrier protein, which makes it faster and specific but no less passive. Doing any of these things is what defines active transport.

Answer: C

Correct answer: both (a) and (b)

Nitrogen fixation needs both. It is enormously expensive in energy - some 16 ATP per N₂ reduced - because the triple bond is so strong. And nitrogenase is irreversibly inactivated by oxygen, so the reaction must take place in an anaerobic setting: a heterocyst, a root nodule protected by leghaemoglobin, or an anaerobic habitat.

Answer: D

Correct answer: Both (b) and (c)

Bacteriochlorophyll and chlorophyll differ in their side groups and, as a direct consequence, in their absorption spectra - bacteriochlorophyll absorbs in the near infrared where chlorophyll cannot. What they share is the chelated metal: both hold magnesium at the centre of the ring, so the first statement is false.

Answer: B

Correct answer: enzymes

Sulfur enters the cell chiefly as cysteine and methionine, so a ³⁵S label ends up in proteins, enzymes among them. Nucleic acids contain no sulfur at all, which is exactly what Hershey and Chase exploited when they used ³⁵S to label phage protein and ³²P to label its DNA.

Answer: C

Correct answer: growth factor

A growth factor is an organic compound - a vitamin, an amino acid, a purine or pyrimidine - that an organism must have but cannot make for itself, so it has to be supplied in the medium. Trace elements and micronutrients are inorganic and needed only in minute amounts.

Answer: A

Correct answer: an inorganic environmental reservoir

Every element in a living thing comes ultimately from an inorganic reservoir - the atmosphere, the oceans, the rocks and soil - and returns to it. The sun supplies energy, not matter, which is why energy flows through an ecosystem while elements cycle round it.

Answer: A

Correct answer: photoautotroph

The name states both halves: photo- for light as the energy source, autotroph for CO₂ as the carbon source. Plants, algae and cyanobacteria are photoautotrophs. A photoheterotroph uses light but needs organic carbon; a chemoautotroph fixes CO₂ using energy from inorganic chemical oxidations.

Answer: C

Correct answer: salt

Halophile means salt-loving, and an obligate one cannot grow without a high salt concentration - the extreme haloarchaea require several molar NaCl and lyse in fresh water. Their cytoplasm is kept osmotically balanced by accumulating potassium ions or compatible solutes.

Answer: C

Correct answer: minerals and CO2

A chemoautotroph takes its energy from oxidising an inorganic compound such as ammonia, nitrite, sulfide or ferrous iron, and its carbon from CO₂. So it needs minerals and CO₂ and nothing organic at all - which is what lets such organisms colonise bare rock and deep-sea vents.

Answer: B

Correct answer: they require inorganic nutrients

Every organism needs inorganic nutrients - water, and sources of nitrogen, phosphorus, sulfur, potassium and the trace metals. The other three are not universal: autotrophs need no organic carbon, many organisms make all their own growth factors, and anaerobes are poisoned by oxygen.